The present invention concerns a method of making stable water-in-oil emulsions having intact lipid vesicles as part of the water or aqueous phase. These water-in-oil emulsions are primarily useful for the cosmetic industry but may also be used in other industries such as food manufacturing, e.g., the making of margarine, and pharmaceutical manufacturing.
Water-in-oil emulsions have discrete droplets of water or an aqueous solvent, called the "discontinuous phase," dispersed in a "continuous Phase" of oil. Oils useful in this type of emulsion include a broad spectrum of water-immiscible materials such as mineral oils, silicone oils, and triglycerides. Water-in-oil emulsions are distinct from oil-in-water emulsions where water forms the continuous phase and oil droplets form the discontinuous phase. Oil-in-water emulsions are more common since they are easier to establish and can be stabilized by use of many different surfactants. In contrast, water-in-oil emulsions are more difficult to establish (assuming there is a significant amount of an aqueous phase) and are often less stable. In addition, the conditions normally used to establish the water-in-oil emulsions are more rigorous than those required for oil-in-water emulsions.
Oil-in-water emulsions containing lipid vesicles have been known for many years. For example, U.S. Pat. No. 3,957,971 describes a variety of emulsions using phospholipid vesicles, i.e., liposomes, as an initial ingredient. While most of the Examples shown in this patent concern the use of suspensions of the liposomes as skin moisturizers, certain of the later Examples, particularly Examples 16 and 17, describe a hand lotion or hand cream made using these liposomes. From the description, it is unclear whether these latter Examples are water-in-oil or oil-in-water emulsions. However, it is unlikely that there are any lipid vesicles remaining because the conditions described to make the hand lotion and hand cream include high shear at high temperature, procedures which are likely to destroy any lipid vesicles.
Two United Kingdom patent applications, U.K. Patent Application Serial No. GB2079179A and U.K. Patent Application Serial No. GB2078534, concern cosmetic preparations having lipid vesicles to stabilize a water-immiscible or oily phase dispersed in an aqueous phase. These patent applications, which are assigned to L'Oreal, are specifically directed to oil-in-water emulsions rather than water-in-oil emulsions.
If any water-in-oil emulsion is deposited on the skin, the water droplets coalesce amid a film of oil. This film protects the skin from noxious agents or irritants, and helps keep the skin hydrated. Another advantage of water-in-oil emulsions is that the emulsifiers normally used in these emulsions do not cause detergent action on the skin. This is in contrast to the emulsifiers used in oil-in-water emulsions which are typically detergent-based and therefore are hygroscopic. Water-in-oil emulsions have better moisturizing properties in that they help reduce transepidermal water loss and chapping. In addition, the oil phase tends to emulsify dirt and sebum on the skin.
One possible use for water-in-oil emulsions is in a sun screen. Because these emulsions are non-hygroscopic, they do not easily take up water and thus are not easily washed off. Accordingly, they are essentially moisture-proof.
Water-in-oil emulsions also have uses outside the cosmetic area. For example, water-in-oil emulsions are used in the manufacture of margarines. U.S. Pat. No. 4,521,440, issued Jun. 4, 1985, concerns making print margarines in the form of water-in-oil emulsions with a structured lipid as the triglyceride forming the primary oil. Although this patent does not concern or suggest the use of lipid vesicles in the emulsion, there is no reason why lipid vesicles could not be used in a margarine if the materials making the vesicles are GRAS products. Further, the emulsion could be used in pharmaceutical manufacturing as well as parenteral and enteral nutrition formulas.
Accordingly, an object of the invention is to provide a method of making a water-in-oil emulsion having intact lipid vesicles as part of the emulsion.
A further object of the invention is to provide cosmetics and other useful products having water-in-oil emulsions with intact vesicles dispersed therein.
Another object of the invention is to provide a stable water-in-oil emulsion having intact non-phospholipid vesicles in the aqueous phase.
These and other objects and features of the invention will be apparent from the following description.